Reintroduce changes #19723 and #19723 that were not

[p5sagit/p5-mst-13.2.git] / lib / ExtUtils / MakeMaker / FAQ.pod

package ExtUtils::MakeMaker::FAQ;

(our $VERSION) = sprintf "%03d", q$Revision: 1.7 $ =~ /Revision:\s+(\S+)/;

1;
__END__

=head1 NAME

ExtUtils::MakeMaker::FAQ - Frequently Asked Questions About MakeMaker

=head1 DESCRIPTION

FAQs, tricks and tips for C<ExtUtils::MakeMaker>.

=head2 Philosophy and History

=over 4

=item Why not just use <insert other build config tool here>?

Why did MakeMaker reinvent the build configuration wheel?  Why not
just use autoconf or automake or ppm or Ant or ...

There are many reasons, but the major one is cross-platform
compatibility.

Perl is one of the most ported pieces of software ever.  It works on
operating systems I've never even heard of (see perlport for details).
It needs a build tool that can work on all those platforms and with
any wacky C compilers they might have.

No such build tool existed at the time and I only know of one now
(Module::Build).


=item What's Module::Build and how does it relate to MakeMaker?

Module::Build is a project by Ken Williams to supplant MakeMaker.
Its primary advantages are:

=over 8

=item * pure perl.  no make, no shell commands

=item * easier to customize

=item * cleaner internals

=item * less cruft

=back

Module::Build is the official heir apparent to MakeMaker and we
encourage people to work on M::B rather than spending time improving
MakeMaker.

=back

=head2 Module Writing

=over 4

=item

How do I keep my $VERSION up to date without resetting it manually?

Often you want to manually set the $VERSION in the main module
distribution because this is the version that everybody sees on CPAN
and maybe you want to customize it a bit.  But for all the other
modules in your dist, $VERSION is really just bookkeeping and all that's
important is it goes up every time the module is changed.  Doing this
by hand is a pain and you often forget.

Simplest way to do it automatically is to use your version control
system's revision number (you are using version control, right?).

In CVS and RCS you use $Z<>Revision$ writing it like so:

    $VERSION = sprintf "%d.%03d", q$Revision$ =~ /(\d+)/g;

On your next check in, $Z<>Revision$ will magically be expanded to contain
the current revision #.

    $VERSION = sprintf "%d.%03d", q$Revision: 1.7 $ =~ /(\d+)/g;

Every time the file is checked in the $Z<>Revision$ will be updated,
updating your $VERSION.

In CVS version 1.9 is followed by 1.10.  Since CPAN compares version
numbers numerically we use a sprintf() to convert 1.9 to 1.009 and
1.10 to 1.010 which compare properly.

If branches are involved (ie. $Z<>Revision: 1.5.3.4) its a little more
complicated.

    # must be all on one line or MakeMaker will get confused.
    $VERSION = do { my @r = (q$Revision$ =~ /\d+/g); sprintf "%d."."%03d" x $#r, @r };

=item

What's this F<META.yml> thing and how did it get in my F<MANIFEST>?!

F<META.yml> is a module meta-data file pioneered by Module::Build and
automatically generated as part of the 'distdir' target (and thus
'dist').  See L<ExtUtils::MakeMaker/"Module Meta-Data">.

To shut off its generation, pass the C<NO_META> flag to C<WriteMakefile()>.

=back

=head2 XS

=over 4

=item

How to I prevent "object version X.XX does not match bootstrap parameter Y.YY"
errors?

XS code is very sensitive to the module version number and will
complain if the version number in your Perl module doesn't match.  If
you change your module's version # without reruning Makefile.PL the old
version number will remain in the Makefile causing the XS code to be built
with the wrong number.

To avoid this, you can force the Makefile to be rebuilt whenever you
change the module containing the version number by adding this to your
WriteMakefile() arguments.

    depend => { '$(FIRST_MAKEFILE)' => '$(VERSION_FROM)' }


=item

How do I make two or more XS files coexist in the same directory?

Sometimes you need to have two and more XS files in the same package.
One way to go is to put them into separate directories, but sometimes
this is not the most suitable solution. The following technique allows
you to put two (and more) XS files in the same directory.

Let's assume that we have a package C<Cool::Foo>, which includes
C<Cool::Foo> and C<Cool::Bar> modules each having a separate XS
file. First we use the following I<Makefile.PL>:

  use ExtUtils::MakeMaker;

  WriteMakefile(
      NAME		=> 'Cool::Foo',
      VERSION_FROM	=> 'Foo.pm',
      OBJECT              => q/$(O_FILES)/,
      # ... other attrs ...
  );

Notice the C<OBJECT> attribute. MakeMaker generates the following
variables in I<Makefile>:

  # Handy lists of source code files:
  XS_FILES= Bar.xs \
  	Foo.xs
  C_FILES = Bar.c \
  	Foo.c
  O_FILES = Bar.o \
  	Foo.o

Therefore we can use the C<O_FILES> variable to tell MakeMaker to use
these objects into the shared library.

That's pretty much it. Now write I<Foo.pm> and I<Foo.xs>, I<Bar.pm>
and I<Bar.xs>, where I<Foo.pm> bootstraps the shared library and
I<Bar.pm> simply loading I<Foo.pm>.

The only issue left is to how to bootstrap I<Bar.xs>. This is done
from I<Foo.xs>:

  MODULE = Cool::Foo PACKAGE = Cool::Foo

  BOOT:
  # boot the second XS file
  boot_Cool__Bar(aTHX_ cv);

If you have more than two files, this is the place where you should
boot extra XS files from.

The following four files sum up all the details discussed so far.

  Foo.pm:
  -------
  package Cool::Foo;

  require DynaLoader;

  our @ISA = qw(DynaLoader);
  our $VERSION = '0.01';
  bootstrap Cool::Foo $VERSION;

  1;

  Bar.pm:
  -------
  package Cool::Bar;

  use Cool::Foo; # bootstraps Bar.xs

  1;

  Foo.xs:
  -------
  #include "EXTERN.h"
  #include "perl.h"
  #include "XSUB.h"

  MODULE = Cool::Foo  PACKAGE = Cool::Foo

  BOOT:
  # boot the second XS file
  boot_Cool__Bar(aTHX_ cv);

  MODULE = Cool::Foo  PACKAGE = Cool::Foo  PREFIX = cool_foo_

  void
  cool_foo_perl_rules()

      CODE:
      fprintf(stderr, "Cool::Foo says: Perl Rules\n");

  Bar.xs:
  -------
  #include "EXTERN.h"
  #include "perl.h"
  #include "XSUB.h"

  MODULE = Cool::Bar  PACKAGE = Cool::Bar PREFIX = cool_bar_

  void
  cool_bar_perl_rules()

      CODE:
      fprintf(stderr, "Cool::Bar says: Perl Rules\n");

And of course a very basic test:

  test.pl:
  --------
  use Test;
  BEGIN { plan tests => 1 };
  use Cool::Foo;
  use Cool::Bar;
  Cool::Foo::perl_rules();
  Cool::Bar::perl_rules();
  ok 1;

This tip has been brought to you by Nick Ing-Simmons and Stas Bekman.

=back

=head1 PATCHING

If you have a question you'd like to see added to the FAQ (whether or
not you have the answer) please send it to makemaker@perl.org.

=head1 AUTHOR

The denizens of makemaker@perl.org.

=head1 SEE ALSO

L<ExtUtils::MakeMaker>

=cut